A defining feature of all nervous systems is the highly regulated and often rapid transfer of information between cells. The information transfer, known as synaptic transmission, occurs at complex, highly specialized sites (chemical synapses), whose role it is to determine both the qualitative and quantitative features of the signals that are passed on to neighboring neurons. The proposed research seeks to define, and understand the nature of, the signal transduction pathways that regulate neurotransmitter secretion, which is the presynaptic component of synaptic transmission. The research plan focuses on a network of evolutionarily conserved proteins that regulates neurotransmitter secretion in the model organism C. elegans: the Go-Gq signaling network. The three major parts of the proposal merge classical genetic studies with a variety of complementary molecular and biochemical approaches in order to understand how this network functions at both genetic and biochemical levels. Part 1 describes strategies to investigate the function of the novel, conserved protein RIC-8 and its relationship to various upstream components of the Go-Gq network. Part 2 describes a variety of strategies that will be used to investigate four "new" genes that were identified in previous genetic screens. These genes appear to encode additional proteins that are involved in the proper function of the Go-Gq network or an interacting pathway. Part 3 describes additional genetic and molecular approaches that will be used to identify other proteins that are part of, or interact with, the Go-Gq network. By discovering new principles about how synaptic transmission is regulated, this research could yield important insights into how nervous systems establish, maintain, and modify behavior. These new principles may ultimately be applicable to the investigation of human neurological disorders.